Study On Harmonic Suppression Method Of Grid Connected Microgrid Based On Active Power Filter

The development of the world economy is accompanied by the increasing demand for all kinds of energy.The excessive exploitation and use of fossil fuels has led to problems such as energy crisis and ecological environment pollution.As an important direction of China’s future energy development,microgrid has the advantages of low energy consumption and low pollution.Through the development of microgrid and the optimization of power quality,it can effectively promote the access of distributed power sources(such as wind power,photovoltaic,etc.)to the large power grid,establish a multi energy system,realize the reliable power supply to the load,and make effective use of renewable energy.It can not only make rational use of natural resources,but also reduce the consumption of traditional fossil energy,and achieve green development to the greatest extent.With the development of science and technology,while the energy storage cost is reduced,the regulation technology of microgrid is also improved,which reduces the cost of microgrid,which means its better development prospect.As the main energy source in microgrid,distributed generation needs to transform the output electric energy.Because it contains large number of power electronic converter devices,it will produce problems such as randomness,large fluctuation range and high-order harmonics in the process of electric energy output,which seriously affect the power quality,especially the problem of harmonics,Therefore,it is of great practical significance to further study the harmonic problem of microgrid.Firstly,this paper expounds the basic structures of two common microgrids,and understands the main causes of harmonics through the research and analysis of the mathematical model of microgrid.Secondly,the conventional microgrid harmonic detection methods are discussed,and the harmonic detection methods such as adaptive algorithm,neural network method,p-q method and i_p-i_qmethod based on instantaneous reactive power theory are introduced in detail.Finally,through comparative analysis,the i_p-i_qmethod with more accurate detection results under asymmetric voltage or distortion is selected to realize harmonic detection.Then,the working principle of active power filter is described,and the widely used hysteresis comparison control method is used to control harmonics.The hysteresis comparison control method is simple and belongs to real-time control.It transmits the difference between the compensation current signal and the actual output current to the hysteresis comparator,and then compares the difference with the allowable error.If it exceeds the allowable error,it will drive the main circuit through the size and direction of the difference.The simulation models of i_p-i_qdetection method and p-q detection method are built by using MATLAB/Simulink software,and the two detection methods are compared and analyzed.The simulation results show that i_p-i_qmethod can still better separate the harmonic current component when the grid voltage is distorted,which is more widely applicable than p-q method.In this paper,hysteresis comparison control method and RBF neural network predictive control method are used to track and control the harmonic current respectively.The simulation results show that at 0.4s,two control methods are used to suppress the harmonic,and the suppression effect is obvious;However,if the two control methods are used to suppress harmonics at the zero time stage,there will be a half cycle time delay only when the hysteresis comparison control method is used,and the RBF neural network predictive control method does not have the above time delay problem.Finally,the active power filter combined with i_p-i_qdetection method and RBF neural network predictive control method is used to simulate the harmonic suppression of the system,which verifies the effectiveness of the harmonic suppression method for microgrid harmonic suppression.